1. Field of the Invention
The present invention relates to a transmission mounted in a vehicle.
2. Description of the Related Art
Heretofore, various kinds of transmission systems have been used in vehicle drive systems, one of which is a manual transmission (hereinafter referred to as “MT”) system whereby a driver changes a transmission gear using a clutch lever and change pedal (shift pedal).
There are also cases in which an automatic transmission (“AT”) system is used whereby a shift actuator is driven automatically, and a transmission gear change is performed according to the vehicle speed, engine rotation speed, or the like. With this AT system, a torque converter type AT that combines a torque converter and a planetary gear and performs gear changing automatically by hydraulic control is used in most vehicles. With a torque converter type AT, gear change timing is set precisely by computer control based on various factors such as adjustment of accelerator depression, vehicle speed, and so forth.
AT systems also include an automated manual transmission (hereinafter referred to as “AMT”) system in which only clutch operation is automated, and a manual-selection multi-speed transmission is combined in which a clutch and gearbox have the same kind of structure as in an MT system.
An AMT system is also called a semi-automatic transmission system, as only clutch operation is automatic, and a driver performs gear selection by normal MT system operation. That is, the shift actuator is driven and a transmission gear is changed by command of a driver.
Presently, an AMT mounted in a passenger car also performs gear selection automatically by controlling throttle opening and clutch and gearbox actuators by by-wire control (electronic control). Furthermore, a dual clutch automated manual transmission (DCT), which is an automatic transmission that has a clutch having two power transmission paths, is also known as a transmission mounted in an automobile.
There is also a type of vehicle in which different transmission systems can be selected, as described in Japanese Patent Application Laid-Open No. 4150481, for example. According to Japanese Patent Application Laid-Open No. 4150481, a transmission system can be selected from a semi-automatic transmission system and a fully automatic transmission system.
With an AT system, an AMT system, and a DCT system, driving is simpler than with an MT system as the clutch operation is generally automated and the clutch operation by a driver is eliminated.
In recent years, the following demands have arisen concerning gear changing in an AT or an AMT type of transmission, (1) a driving force to be restored by engaging the clutch gently, (2) a driving force to be adjusted without changing gears in a traffic jam or the like, and (3) a fast start.
That is, there is a demand for a driver to be able to perform clutch engagement/disengagement or half-clutch adjustment operation in order to (1) adjust the degree of restoration of driving force when changing gears, (2) adjust driving force without a gear change, and (3) adjust driving force when setting off, for instance.
With a motorcycle, in particular, it is preferable to adjust the driving force output via the transmission when cornering. Specifically, when making a tight turn, the vehicle can be banked by disengaging the clutch, and there is a demand to be able to make an appropriate turn using this operation. Also, there is a demand to be able to perform clutch operation in order to lower the front wheel by adjusting the driving force when performing a wheelie when setting off.